Chitin demineralization

Source of chitin Demineralization process Deproteinization process References... 

Further reduction in cost of the chitinous supplement was achieved in two experiments with young ruminating neifers where we supplemented whey-rich rations with raw and demineralized crab meals (91.). Statistical analysis showed no significant dietary effect on net weight gain or feed efficiency for either experiment. Diarrhea increased by including whey alone in the ration. In contrast, the inclusion of either raw or demineralized crab meal alone in trie ration induced constipation. The addition of crab meal and whey to the ration restored feces to normal. 

FIGURE 2.18 The Raman spectra of (a) a-chitin and (b, c, and d) demineralized samples using different acid solutions (see Table 2.9). 

TABLE 2.10 Demineralization procedures used for different samples of a-chitin... 

There are many traditional methods for isolation of chitin oligomers. The procedures involved acid hydrolysis, neutralization, demineralization, fractionation by charcoal-celite column, fractionation by high-performance liquid chromatography (HPLC), and lyophilization. 

Chitin is a homopolymer of AT-acetyl-D-glucosamine residues and is a major structural component in the exoskeletons of crustaceans, mollusks, arthropods, and the cell walls of numerous fungi and algae. Owing to its widespread presence in both terrestrial and aquatic organisms, chitin is second only to cellulose as the most abundant biopolymer on the Earth (Shahidi and Abuzaytoun, 2005). On a dry weight basis, shrimp, crab, lobster, prawn, and crayfish have been reported to contain between 14% and 35% chitin, while deproteinized dry shell waste of Antarctic krill contains approximately 40% crude chitin (Haard et al, 1994). Crustaceans are the primary sources of chitin used in industry. Chitin can be extracted from shellfish and crustacean waste by mixing with a dilute add to induce demineralization, followed by a deproteini-zation step in a hot alkaline solution (Synowiecki and Al-Khateeb, 2003). 

One of the most studied biosorbent is chitin, which is an abundant biopolymer found in crustaceans, insects and fungus. This biopolymer is commercially purified by alkaline deproteinization, acid demineralization and decoloration by organic solvents of crustaceans wastes (Pastor, 2004). An additional stronger alkaline treatment of chitin produces deacetylated chitin. If the acetylation degree (DA) decreases at 39% or less, the biopolymer is named chitosan. Hence, the DA of chitin is variable and depends on the process conditions (alkali concentration, contact time, temperature, etc.), which produces DA values from 100 to 0%. Because of this, chitin is known as the biopolymer which has a DA from 100 to 40% likewise, when the chitinous biopolymer has DA lower than 40%, the biopolymer is named chitosan. Chitosan is, therefore, a biopolymer with structure very similar to that of chitin (see Figure 2) however, chitosan solubility is much greater, especially in acid mediums. 

Chitin, Chitosan, Demineralization, Deproteinization, Deacetylation, Degree of acetylation. Metal ions complexation. Polyelectrolyte complex. Biomaterial, Rocculation, Antimicrobial activity... 

Chitin isolation processes are generally performed through the following consecutive steps raw material conditioning, protein extraction (deproteinization), removal of inorganic components (demineralization) and decolouration. This sequence is preferred if the isolated protein is to be used as food additive for livestock feeding. Otherwise, demineralization can be carried out first [10]. A brief account of these processes will be given below. A more detailed description of chitin isolation (and chitosan preparation) can be found elsewhere [5, 8, 11]. 

It is evident that if the amount of acid employed is below the stoichiometric ratio, the demineralization reaction will not be completed. The acid concentration and the reaction time depend on the source, but these parameters must be carefully controlled in order to minimize the hydrol3dic depolymerization and deacetylation of chitin. High temperature treatments must also be avoided to prevent thermal degradation [10]. An alternative treatment for demineralization makes use of the complexing agent EDTA (ethylenediamine tetra acetic acid) in basic media [15]. 

Paulino et al. (2006) obtained chitin with high purity from silkworm pupa, but the yield of chitin and chitosan were low when compared with the chitin and chitosan produced from aquatic crustacean shells. The lower yield of chitin may be due to the effect of treatment on insect materials with HCl at high temperature (Table 1.1). Therefore, it should be considered that the process of acid demineralization step is to be carried out under mild condition, which can avoid the possibility... 

The isolation of chitin from shellfish waste consists of three steps deproteinization (DP), demineralization (DM), and decolorization (DC) whereby the order of the first two steps is generally considered irrelevant if protein or pigment recovery is not an objective (Shahidi and Synowiecki 1991). Chitin is further deacetylated (DA) to make chitosan or other products for a wide array of applications. Both chemical and enzymatic non-continuous batch methods are widely used on an industrial scale for the production of chitin, chitosan, and COS. 

Teng et al. (2001) reported that proteolytic fungal fermentation of shrimp shells is a simple, effective, and inexpensive approach of chitin production from shrimp shells and fnngal mycelia. The results suggest that deproteinization and demineralization occnrs nnder those conditions. Sini et al. (2007) reported that Bacillus subtilis is an efficient starter cnltme from fermentation of shrimp shells. About 84% of the protein and 72% of the minerals were ranoved from the fermented residne at the end of fermentation. 

The yield of chitin was 15-20%. In this case, the protein layer was unprotected because the deproteinization precedes the decalcification. That is why during demineralization more hydrolysis and loss of material in the solid chitin fraction occurred... 

In terms of improving the quality of chitosan, partial autolysis plays a crucial role because it facilitates exposure of CaC03 directly to the chemicals used during the demineralization process. For the industrial practice of chitin extraction, this means that a shorter time and lower concentration of HCl may be adequate to demineralize and thus avoid damage due to the hydrolytic action of HCl on the polymeric backbone structure of chitin. However, it was found that the protein content after treatment of autolyzed biomaterial with 2% NaOH was similar to the protein content after standard 4% NaOH treatment. Obviously, this study could help... 

Keeping in mind the importance of chitosan, as well as its economic value as an industrial product, we must pay attention to its key physical parameter, i.e., turbidity. Depending on source, a marked difference is observed in aqueous solutions of chitosan and its derivatives in terms of their turbidity [33]. Turbid aqueous solutions of chitosan and chitosan-derived products greatly lose their commercial value. Such chitosan cannot be used as a commercial product and in some cases may have to be discarded. Therefore, the selection of source plays a pivotal role in the production of chitin and chitosan. Shepherd et al. [20] reported the production of chitosan from New Zealand Arrow squid Notodarus sloani) pens as well as the evaluation of the functional properties of this squid chitosan compared with chitosan extracted from crustacean sources. Squid pen chitin and chitosan were visibly cleaner than chitin and chitosan obtained from crab and crayfish. In addition, due to the lower mineral content of squid pen as compared to cmstacean shells, the demineralization process can be skipped to extract chitin, which also makes the production cheaper. As shown in Table 4, the squid pen chitosan is similar in... 

Mahmoud NS, Ghaly AE, Arab F (2007) Unconventional approach for demineralization of deproteinized crustacean shells for chitin production. Am J Biochem Biotechnol 3 1-9... 

Chitin and chitosan rarely occur in a pure, easily isolated form. A substantial effort has been made to develop chemical, mechanical, and enzymatic methods to obtain purified materials (25). The usual method of obtaining chitin involves the chemical treatment of shell fish wastes from the crab and shrimp industries. The first step is to demineralize the shell with dilute hydrochloric acid at room temperature. This is followed with a deproteinization step with warm dilute caustic. This yields a partially deacetylated chitin, which may then be further deacetylated to chitosan. Figure 3 shows the underlying chitin matrix in the crab shell and its microfibrillar... 

Broadly, the three different steps involved in the preparation of chitin from crustacean shells can be classified as demineralization, deproteinization and decoloration, which is then followed by its alkaline deacetylation for the synthesis of chitosan [10,11]. Briefly, the outer crustacean shells are initially removed from the shrimps and crabs and washed with cold water, dried in the sun and demineralized with 1.25 N HCl at room temperature. The shells are then washed with water to remove acid and calcium chloride. They are then deproteinated by boiling with 5% sodium hydroxide (NaOH) for 15 min. This process of deproteinization is repeated to completely remove the protein content from the shells and then washed with water to neutrality. It is then decolorized with acetone to remove the remaining pigments and the resultant product is chitin, which is then dried imder the sun [12,13],... 

Chitin is a naturally occurring polysaccharide existing in the outer shells of crustaceans, insect exoskeletons, and fungal ceU walls. It is the second most abundant natural polymer after cellulose. Chitin is commercially produced from the shell waste of crabs, shrimps, and kriUs through a series of deproteinization and demineralization processes to remove the protein and minerals, which together with chitin form the composite structure of the shells. The dry mass of shell waste typically contains about 15-25% of chitin. 

The production of chitin involves the treatment of raw materials with dilute acid for demineralization (removal of especially CaC03) and with dilute alkali to remove the proteins. Chitin can be deacetylated using hot and concentrated alkali to form chitosan. 

Two routes for purification of shrimp shells to obtain chitin whiskers were evaluated. The best result was found when demineralization was performed with IM HCL followed by sample deproteinization with 5% w/v KOH. In order to obtain chitin whiskers an acidic hydrolysis was performed with several acids HCL, H2SO4 and H3PO4. Chitin whiskers with lengths between 90 and 170 nm were obtained with phosphoric acid. The process was evaluated by FTIR, TGA and TEM. 

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